This invention relates to an on-vehicle navigation system which calculates the geographical position of a vehicle from the planned heading and running distance of the vehicle and which displays the calculated position.
A technique of the specified type has heretofore been, for example, one described in Japanese Patent Application Publication No. 59-28244 wherein a road map is set on a display device, and the changing position of a vehicle is displayed in superposition on the road map through the detection of the heading of the vehicle and the detection of the running distance thereof. A unit running distance of the vehicle is set shorter than a distance corresponding to the basic display interval of the display device in each of the X- and Y-directions thereof, X- and Y-direction components in the running of every unit distance are calculated on the basis of a vehicular detection output so as to cumulatively add and subtract such respective components, and when the cumulative value has reached the distance corresponding to the basic display interval, the display spot of the display device in the X-direction or Y-direction thereof is shifted by one unit.
With the prior art constructed as described above, the errors of the cumulative values of the X- and Y-direction components are small in running within a zone of comparatively small area, but they enlarge in running over a large zone. More specifically, in a case where a vehicle runs from a starting location (a) and along a course (a)-(b)-(c)-(d)-(a) as illustrated in FIG. 10, the lengths of the latitudinal parallels I.sub.1 and I.sub.2 lying between the longitudinal meridians K.sub.1 and K.sub.2 are unequal to each other. This leads to the problem that, reven when the vehicle has returned to the starting location (a) after making a round of the course (a)-(b)-(c)-(d)-(a), the calculated value does not agree with the value of the starting location (a), so the disagreement of the display spot arises also on the display device.